Method of and apparatus for sound recording



Aug. 1 940. M. c. BATSEL 2.210.392

METHOD OF AND APPARATUS FOR SOUND RECORDING Filed Dec. 30, 1958 I Snnentor (It torneg Patented Aug. 6, 1940 AND APPARATUSFOR. SOUND RECORDING v UNI-TED" STATES- METl-IOD or I I -2,210,39-2 PATENT orrlcs Max 0. Batsel, Haddonfield,,-N.- 1., assignor to Radio Corporation of America, a corporation I of Delaware 7 Application December 30, 1938, Serial No. 248,394

.2 Claims.

This invention relates tea-method of and apparatus for recording sound by what is known as the variable density method, and more particularly to the species thereof known as ,squeeze track recording: Squeeze track recording is known in the prior art in the form of apparatus 7 where masks are inserted in the light beam to limit the effective track widthin variable den,- sity recording. Such apparatus is subject to certain practical limitations due to the fact that the operator thereof, is not. always able to accurately 'forecast the trackwidth necessary, and, also, the

adjustment of changes in track width are necessarily more or less abrupt.

' According to the present invention, I maintain the amplitude of the signal applied to the recording galvanomet'er or equivalent light control apparatus substantially constant, and vary the track width by means of electrically controlled shutters in proportion to the loudness of the sound, In the recording, the volume of the re-' corded sound is controlled automatically to bring it to a constant average level, while the track width control shutters are operated in a manner complementary to the operation of the volume control so that when the volume of loud sounds is decreased to bring them to the constant amplitude, the track width control shutters are moved apart a corresponding amount to provide increased available volume on the sound recording, and conversely when a relatively soft sound is amplified to bring it up to average level, the shutters are moved toward each other to give a lessened track width.

The invention, of course, is not limitedv to the use of a perfectly constant average amplitude of modulation of the galvanometer. or'equivalent device nor'to the use of two shutters. Asingle shutter OfmOdlfiEd shapes of shutters such as are well known in the art, may beused to produce the desired. control of track width. The volume control, andthe corresponding shutter control may be accomplished with any desired degree oflinearity or non-linearity inrelation to the amplitudeof the sound. l 7

Likewise the invention is not limited to the regulation of a volume control shutter in a direct relation with the recorded volume, but the shut: ter may be caused to move a greater or less amount than that which would be proportional to the volume ohanges'in the recorded sound, thereby producing'either volume expansion or volume compress-ion. 7

One object of the invention is to provide an im- 55 proved apparatus for variable density sound recording.

Another, object of the invention is to provide an improved method for variable density sound recording. v

Another object of the, invention is to provide a similar devices.

(01. lie- 100.3

method of and apparatus for variable density sound recording in which the volume level of the recorded sound may be maintained constant or in any desired-ratio to the volume range of the sound recorded.

I Another object of 'theinventionis to provide 1 an improved apparatus for recording sound by what is known as the penumbra method.

Another object of myinvention is to. provide an improved apparatus for producingwhat is known as a squeeze sound track record. 1 Y Other and incidental" objects of my invention will be apparentto those skilled in the art from a reading, of the following specification. and an inspection of the accompanying drawing in which Figureil is a schematic diagram of myimproved.

apparatus showing portions of the optical systemthere'of in perspective,

Figure 2 is a schematic diagram showing a modified form of the invention, and

Figure 3 is a plan view of the optical system used in the apparatus.

Referring first to Fig. 1, which shows the preferred form of the invention, the sound to be recorded is impressed on themicrophone indicated at Ill and is transmitted to the amplifier II.

This amplifier may be of any customary type such as those usually used in sound recording. The audio frequency outputfrom the amplifier ll is transmitted to the automatic volume control device l3. This device is not shown in detail as automatic volume controls are well known in the art and are customary in radio receivers and v This automatic volume control brings the electrical impulses corresponding 'to the sounds to a substantially constant average value. If desired, this volume control device may,

instead of bringing the soundsto a uniformaverage value, merely reduce the range of their volume to within predetermined limits or in a predetermined ratio to the loudness of the original sounds, the essential featurebeing that it will materially decrease thevolume range of the output impulses as compared with the volume range of" the sounds impressed upon the microphone H1. The output iromthe AVC device I3 is transmitted to a galvanometer l2 having a mirror 25 adapted to be vibrated in accordance with the acoustic impulses transmitted to the galvanome The output from the amplifier M is directed to.

the magnet or magnets I5 of the shutters I6 and The optical system used as shown in Figs. 1'

and 3 is preferablyof the penumbra type for variable density recording such as described on pages 270-273 of the Journal of the Society of Motion Picture Engineers for September 1937. In this optical system, light'from the exciter lamp passes through the cylindrical lens 2I and the spherical lens 22 to the penumbra aperture 23, adjacent which'an image of the filament of the lamp 20 is formed in such relation as to provide a graduated illumination of the aperture in the plate 23. An image of the aperture in the plate 23 is formed upon the slit plate 26 by the lens 24, the light being reflected from the galvanometer mirror by which it is vibrated in accordance with the sound waves. A condenser lens 30 is provided adjacent the slit plate for increasing the illumination transmitted therethrough.

Between the lens 2| and 22 and the aperture plate 23 there is provided an aperture plate 29 adjacent to which are located the shutters l8 and I1 actuated by the magnetic means it from the amplifier I 4. These shutters move transversely across the aperture in the plate 25 in accordance with the volume of the sound as above described, thereby varying the width of the image formed upon the'slit plate 26. The objective lens 2! focuses a linear image of the light passing through the slit plate 27 upon the film'Zfl. .The preferred type of shutter mechanism is described in detail and is claimed in Hasbrouck Patent 2,102,778, issuedDecember 21, 1937. r

The amplifier I4 is so connected to the shutter mechanism I5, I6, I! that when the amplitude of the sounds to be recorded decreases, the shutters are moved toward each other or if a single shutter or a V-shaped shutter were used, the shutter would be moved correspondingly toward a position where the sound track width would be a minimum, thereby decreasing the sound track width in appropriate ratio to the decrease in amplitude of the sound. As pointed out above, this movement of the shutters may be so chosen as to give volume compression or volume expansion or to merely control the sound track width directly in accordance with the volume range. It will be apparent that this change in sound track width varies proportionately the amount of light transmitted thereto in recording and accordingly the amount of light transmitted therethrough in reproduction of a positive print.

The foregoing arrangement permits the density modulation of the sound track in accordance with the sound frequencies to be maintained at an optimum value or between desired limits producing the most desirable values of exposure in the ecording, while at the same time providing adequate volume range. The arrangement further may substantially eliminate manual volume control during recording.

If desired, additional noise reduction may be accomplished by the usual method ofv keeping the .to give considerable attenuation.

with the construction or operation of the appa- .ratus.

If it is desired to control the apparatus manually instead of automatically, the arrangement shown in Fig. 2 may be used.

In this arrangement the microphone I0 and main amplifier II are provided as in the first arrangement, but attenuator 32 is substituted for the automatic volume control I 3. This attenuator, like the automatic volumecontrol, lowers the impulses from the amplifier II to the galvanometer I2 to a predetermined level but instead of this level being fixed, it may be manually adjusted by means of a control knob 35. If the sound to be recorded is expected to be very low in level, the knob is so adjusted as to give very little attenuation, or if the sound is expected to be very high in level, the attenuator is adjusted In order to 0perate the shutter mechanism I5, an appropriate source of power such as the battery 33 is provided together with a control means, such as a potentiometer 34. A series resistor, of course, may be substituted if desired for the potentiometer. In either event, the control means 34 serves tocontrol the current through the magnets of the shutters I6 and I1, thereby determining the track width to be used. As indicated in the drawing, the attenuator 32 is interconnected with the shutter control 34 so that at any degree of attenuation an inversely corresponding track width is provided. If loud sounds are being recorded they are considerably attenuated and a relatively large track'width is used, and conversely on faint sounds'the attenuation is very slight, but a narrow track is used. It will be apparent to those skilled in the art that in either of the above described arrangements the sound track width is controlled in pro portion to the volume of the sounds being recorded, while the sound volumes as applied to the recording galvanometer are reduced to a more or less uniform level and that in both cases the variation in sound track width is. maintained in a predetermined ratio to the variation in amplitude transmitted to the galvanometer.

Having now described my invention, I claim:

1. A sound recording apparatus including means for producing a variable density sound record at a constant amplitude level from impulses at varying amplitude levels, and means for controlling the area of said record in accordance with the envelope of said impulses at varying amplitude levels, said means including shutters movable inwardly from the edges of the record.

2. A sound recording apparatus including an amplifier, automatic volume control means for maintaining the output of said amplifier at a substantially constant level, means for recording said constant level output as a variable density record, and independent means including shutters movable inwardly from the edges of the rec- 0rd controlled by the output of saidamplifier for controlling the area of said record in accordance with the output of said amplifier.

MAX C. BA'I'SEL. 

